Kinematic modeling and calibration of a Stewart platform

Manufacturing tolerances, installation errors and link offsets contaminate kinematic parameters of a nominal platform kinematic model. Since the platform controller determines the length of the leg actuators according to the nominal model, the resulting pose of the platform is inaccurate. To enhance the positioning accuracy of the platform, there is a need to estimate the actual values of these parameters and to incorporate these estimates into the inverse kinematic procedure performed by the machine controller. The objective of this paper is 2-fold. First, a new kinematic model is proposed to represent the errors due to imperfection of the U-joints and the ball-joints, which are key components of the Stewart platform. This model may be used to assist the design of the Stewart platform as the effects of mechanical tolerances of different components on the system accuracy can be fully explored. Secondly, an error-model-based method is devised for Stewart platform calibration, by which the accuracy of the Stewart platform can be greatly improved.